United States Patent Application 2008/0191883 A1 (Imaichi, et al.) describes a resonant tag for use with a radio-wave detection system for the prevention of shoplifting or the like which has a coil and capacitor circuit formed on opposite sides of an extremely thin substrate of a biaxially-oriented polypropylene, with one of the capacitor plates formed on one side of the substrate and the coil and other capacitor plate formed on the other side of the substrate, and whereby the circuit can provide the same performance of a conventional resonant tag but using a much smaller size.
U.S. Pat. No. 7,129,843 (Piccoli, et al.) describes a security tag that includes a combination of a resonant frequency circuit with an adjacent amplification shield for enhancing output signal amplitude. The amplification shield is located adjacent to the resonant frequency circuit and is preferably in the same or substantially the same plane as the resonant frequency circuit or is in a close, generally parallel plane. In an exemplary embodiment, the resonant frequency circuit includes an inductor electrically coupled to a capacitor. The resonant frequency circuit has a center frequency and is arranged to resonate in response to exposure to electromagnetic energy at or near the center frequency, providing an output signal having an amplitude. The amplification shield is arranged to direct a portion of the electromagnetic energy to the resonant frequency circuit to amplify the amplitude of the output signal from the resonant frequency circuit.
Notably, FIG. 2 of the Piccoli et al. patent depicts conductive traces in the interior of the loop. Among these traces are multiple dots. These are electrically inert at the resonant frequency of the tag depicted. Presumably their only purpose is to reduce the amount of chemicals required to achieve the desired pattern when the pattern is created by etching a solid sheet of metal or other conductor. Also depicted is a “trimmable” segment of capacitor tuning “fingers.” The exact resonant frequency of the circuit can be adjusted by cutting or ablating this structure at a selected location.
U.S. Patent Application Publication No. 2008/0150719 (Cote, et al.) describes a combination EAS and UHF security tag that adds the ability to add item level UHF functionality to a retail tag and maintain the integrity of the EAS systems installed in the business and whereby the EAS and UHF security elements are substantially formed from a common conductive layer. This combination tag also includes the ability to change a tag for use as a “far-field read” tag to use as a “near-field read” tag. U.S. Patent Application Publication No. 2007/0090955 (Cote, et al.) describes a capacitor strap that is applied to a security tag coil or antenna to form and properly tune an EAS or an RFID security tag. The capacitor strap is a thin film capacitor formed of two metal foils, in between which is a dielectric material having ends that are electrically coupled to different points of a security tag coil or antenna. The capacitor strap may include an RFID integrated circuit, either in series or in parallel with the capacitor, which is then applied to security tag coil at a particular location to tune the tag to a predetermined frequency.
While the inventions of the above identified prior art patents appear suitable for their intended purposes, they leave something to be desired from the standpoint of addressing certain process stability and yield concerns, which arise while attempting to make new resonant or combination resonant/UHF security label element circuits with large window areas using newer oriented polymer base materials. In particular, the thinness of the oriented polymer substrate, combined with the use of newer adhesives to clad aluminum or other conductors to the substrate, can lead to undesired process variation or yield fall out do to stretching, stressing, or tearing of portions of manufacturing webs subjected to heat, tension, and/or air or chemical jets.
The subject invention addresses that unmet need by providing mechanical improvements to the elements of the security label/tag. In addition, by providing mechanical improvements to the elements of the label/tag, this invention enables the label/tag to achieve superior multiple frequency response.
All references are incorporated in their entirety.